This invention relates to a subsea tanker hydrocarbon production system.
Much of the exploitation of hydrocarbon deposits is conducted in the realm of deep offshore waters. In fact some of the largest and most prolific such deposits are to be had in deep waters. So deep are these waters that existing subsea hydrocarbon extraction technology is utilised at its very operational limits.
Hitherto there have been two methods of hydrocarbon production offshore. The first utilises platforms raised above wave-height sitting upon concrete and/or steel towers which are themselves fixed to the seabed. Such towers are extraordinarily expensive. The second utilises subsea wellheads and clusters of tied-back subsea wellheads, production from which is conducted via a flexible riser pipe to a floating production station. Although less expensive than a fixed platform, a considerable amount of costly marine infrastructure is required for such an operation. What both of these methods have in common is their production facility, i.e. that which is placed upon the platforms, whether they be fixed or floating. Such a production facility concerns itself with a separation of the produced fluids (the various gas and oil phases, together with any produced associated water) and their subsequent measurement. It is usually the oil (and gas condensate) phases which are most prized, and are despatched to market. In the case of the fixed platforms this despatch is by seabed pipeline, and in case of the floating stations, by ship. The gas phases are often considered as less valuable, and depending on the economics of any particular project and its location, are variously disposed of, via alternative pipelines, re-injected back into the hydrocarbon reservoir rock elsewhere, or simply flared, i.e. burnt. Many authorities consider the flaring of gas phases, a common feature, as unnecessarily wasteful. Whilst such separation is a continuous process, the requirement for measurement is met by the intermittent diversion of production flows from individual wells. This is performed via a smaller and dedicated measuring separation train, and flows so measured are then rerouted back into the continuous process. Whilst the measurement of the productivity of individual wells contributes nothing to immediate economics, such measured data is essential for the extractive management of the hydrocarbon deposit (i.e. the reservoir) as a whole. Further, notwithstanding any financial or technical considerations, such processing operations are notoriously hazardous to personnel.